In resistance welding, the components to be connected are pressed together and are melted electrically by the welding current at the contact point between the components.
In that context, the most significant in practice is resistance spot welding, in which the punctiform electrodes of the welder tongs press the components to be connected directly against one another. Necessary components of resistance welding are welder tongs with the welding electrodes, a source of welding current connected to the welder tongs, which source has a welding transformer, and a welding control unit and, where relevant, a process monitoring system for appropriately controlling the welding process.
In the case of resistance spot welding, the parts to be joined are then usually pressed together pneumatically at the two welding electrodes with a predefined force. Then, the welding current is switched on for the duration of the welding time. The electrical resistance at the contact point between the two parts is then substantially greater than the actual electrical resistance of the materials of the parts to be joined. By means of the punctual thermoelectric heating over the contact resistance achieved thereby, there thus results a lenticular melt. The simultaneous pressure via the electrode force effects a punctual, material-bonded and permanent connection. The electrode force is maintained during a dwell time in order to thus ensure that the melt cools in a manner which avoids the formation of voids.
Steam generator pipes with a turbulence-generating insert are then of use when the flow medium is to be made to flow faster at the internal face of the steam generator pipes. In that context, the use of such internally-ribbed pipes can be necessary for various reasons, e.g. in the case of a low mass flow rate through the evaporator when a power station is at full load. The use of internally-ribbed pipes can also be necessary in the case of high heat flux. In this case there is namely the risk of film boiling, that is to say there forms on the inside of the steam generator pipes a film of steam which, contrary to the thoroughly mixed liquid in the case of nucleate boiling, has a strongly thermally insulating effect. The consequence of this is that, if the heat flux remains the same, the wall temperature can increase markedly, which in turn can lead to the destruction of the heating faces. Last but not least, the internally-ribbed pipes can make it possible to avoid a stratification of the flow (separation of the water and steam phases) in normal load operation.
EP 2 390 567 A1 describes a method in which a turbulence-generating insert is attached in grooves of a template shaft, the template shaft is then inserted with the insert into a steam generator pipe, the insert is detached from the template shaft and the template shaft is then removed again from the steam generator pipe.
EP 2 390 039 A1 describes a device and a method for attaching, in materially-bonded fashion, such a turbulence-generating insert into a steam generator pipe by means of shielding gas welding.